Image forming apparatuses such as printers, facsimiles, copiers, and multi-function machines having the functions of a printer, a facsimile, and a copier, form images by conveying a medium (hereinafter also referred to as “paper”) and applying a liquid (hereinafter also referred to as “recording liquid” or “ink”) onto the medium. In forming the images, the image forming apparatus uses, for example, a liquid applying apparatus (e.g., liquid jet apparatus) including a recording head having a liquid jet head for jetting droplets of liquid (recording liquid). It is to be noted that image forming may also be referred to as recording, printing, image printing, or character printing. It is also to be noted that the material of the medium is not limited to a particular material. Thus, the medium may be also be referred to as a sheet of paper, a target medium, a recording medium, a transfer material, or a recording paper.
The image forming may be performed on a medium made of, for example, paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, or ceramic. Furthermore, the image forming not only includes forming images which have meaning (e.g., characters, shapes) or forming images having no particular meaning (e.g., patterns), but also includes applying (coating) a material having a desired function onto a given area of a target medium. Furthermore, the liquid applying apparatus includes an apparatus that applies a liquid onto a target medium by using, for example, a liquid jet head, a roller, a brush, or a spray. Furthermore, the applied liquid is not limited to a recording liquid (ink). As long as it is a liquid, the applied liquid may also be, for example, a DNA sample, a resist material, a resin material, a patterning material, or a material having a desired function/property (e.g., an illuminating property, a light blocking property, a conductive property, a fixing function, a glossy property, a liquid absorbing function) and is not limited to a recording liquid or ink.
For example, in using an image forming apparatus that forms an image by applying a recording liquid onto a recording medium, the image forming apparatus requires some amount of time for waiting for the recording liquid to dry. Accordingly, during the period of waiting for the drying of the recording liquid, the image forming apparatus may keep the recording medium inside itself after performing the image forming process. In a case where the image forming apparatus performs double-side printing, the recording medium may be temporarily discharged to a sheet discharge tray after performing the image forming process on one side of the recording medium and fed back into the image forming apparatus for performing the image forming process on the other side of the recording medium.
For example, in an image forming apparatus shown in Japanese Registered Patent Publication No. 3109529, there is disclosed a delaying part for delaying the timing of discharging a recording medium for a predetermined period based on a predetermined value set according to the determination results of dot density of a previous recording.
As another example, in an image forming apparatus shown in Japanese Laid-Open Patent Application No. 2000-001010, there is disclosed a configuration of temporarily discharging at least a portion of a sheet of paper outside of the image forming apparatus after printing on one side of the paper in a double-side printing operation for obtaining time for the paper to dry.
As another example, in an image forming apparatus shown in Japanese Laid-Open Patent Application No. 2006-082546, there is disclosed a part that performs a paper discharging operation after a recording medium having an image formed thereon has both ends restrained until curling of the recording medium is unlikely to occur.
As another example, in an image forming apparatus shown in Japanese Laid-Open Patent Application No. 2003-248349, there is disclosed a configuration for temporarily delaying the timing of discharging a sheet of paper having a low fixing property (e.g., OHP) until the temperature of the OHP decreases.
As another example, in an image forming apparatus shown in Japanese Laid-Open Patent Application No. 2005-292651, there is disclosed a fixing apparatus including plural fixing parts for fixing a toner image on a sheet of paper, a roundabout conveying path for conveying the paper around at least one of the fixing parts, a main conveying path for conveying the paper via the roundabout conveying path, and a conveying path switching part for selecting a conveying path at a branching part between the roundabout conveying path and the main conveying path in which the time required for conveying the sheet through the roundabout conveying path is substantially equal to the time required for conveying the sheet through the main conveying path.
As another example, in a liquid applying apparatus using a brush or a roller, a sheet of paper is temporarily discharged from the apparatus until the paper becomes dry.
Meanwhile, in a typical image forming apparatus, a recording liquid having high viscosity (ink having high viscosity) is commonly used for achieving high speed recording and forming high quality images with respect to plain paper. Particularly, in a case where a pigment type ink (e.g., organic pigment, carbon black) is used as a coloring agent, a pigment is usually mixed together with a dispersant and dispersed in a stable state, to thereby obtain an aqueous ink. On the whole, the pigment type ink attains a high viscosity (no less than 5 mPa·s). Thus, in forming an image on plain paper, the pigment type ink exhibits a better quick-drying property than that of the dye type ink. Nevertheless, the pigment type ink has a tendency of causing curling of the recording medium.
More specifically, in using a dye type ink, moisture permeates from the back side of the recording medium to the front side of the recording medium and reduces the moisture difference between the front side of the recording medium and the back side of the recording medium. Therefore, although more drying time is required when using a dye type ink, curling due to moisture difference between the front and back side of the recording medium is relatively less likely to occur. On the other hand, in using a pigment type ink, due to its high quick-drying property, little time is required for the ink to dry. However, since time is required for the ink to sink (soak) into the recording medium, the moisture difference between the front side and the back side of the recording medium increases. This moisture difference leads to curling of the recording medium. In a case where such curl occurs, the recording medium may stiffen in the curled state due to the quick-drying property of the pigment type ink.
Therefore, conveying the recording medium in the curled state may cause jamming and adversely affect sheet-discharging steadiness. This results in a poorly printed recording medium.
Furthermore, although a pigment type ink has a high quick-drying property, smudging due to insufficient drying of ink may occur depending on the formula of ink or the type of paper used. Furthermore, the problem of drying which the pigment type ink faces is more serious in a case of using the dye type ink.
Thus, in a case where an insufficiently dried paper is conveyed, ink stains may adhere to a conveying part of an image forming apparatus. This may cause ink stains of the conveying part to re-adhere to a conveyed paper and cause the stains on the paper to adhere to other paper.
Furthermore, in one example of a liquid jet type image forming apparatus, paper may be flipped over (flipped upside down) and discharged from the liquid forming apparatus in a downward facing manner so that paper can be discharged (stacked) in an order corresponding to the order of printing on the paper. Therefore, in a case where curling occurs, the paper curls in a manner where the side opposite of the recorded side is facing upward, that is, in a manner where the ends of the paper are facing upward. Compared to a case of stacking the paper in a manner where the recorded side is facing upward, it is difficult to stack the paper on a discharged paper stacking part of the image forming apparatus.
Thus, demands for resolving the problems of curling of paper and staining of paper are growing. However, at the same time of resolving such problems, there is also a need to prevent productivity from decreasing due to decrease of throughput caused by correcting the curling or waiting for the drying of paper.